HDL regulates the displacement of hepatic lipase from cell surface proteoglycans and the hydrolysis of VLDL triacylglycerol

We have previously shown that hepatic lipase (HL) is inactive when bound to purified heparan sulfate proteoglycans and can be liberated by HDL and apolipoprotein A-I (apoA-I), but not by LDL or VLDL. In this study, we show that HDL is also able to displace HL directly from the surface of the hepatoma cell line, HepG2, and Chinese hamster ovary cells stably overexpressing human HL. ApoA-I is more efficient at displacing cell surface HL than is HDL, and different HDL classes vary in their ability to displace HL from the cell surface. HDL2s have a greater capacity to remove HL from the cell surface and intracellular compartments, as compared with the smaller HDL particles. The different HDL subclasses also uniquely affect the activity of the enzyme. HDL2 stimulates HL-mediated hydrolysis of VLDL-triacylglycerol, while HDL3 is inhibitory. Inhibition of VLDL hydrolysis appears to result from a decreased interlipoprotein shuttling of HL between VLDL and the smaller, more dense HDL particles. This study suggests that high HDL2 levels are positively related to efficient triacylglycerol hydrolysis by their ability to enhance the liberation of HL into the plasma compartment and by a direct stimulation of VLDL-triacylglycerol hydrolysis.     

Adenovirus E1A,not human papillomavirus E7, sensitizes tumor cells to lysis by macrophages through nitric oxide- and TNF-alpha-dependent mechanisms despite up-regulation of 70-kDa heat shock protein

Expression of adenovirus (Ad) serotype 2 or 5 (Ad2/5) E1A or human papillomavirus (HPV)16 E7 reportedly sensitizes cells to lysis by macrophages. Macrophages possess several mechanisms to kill tumor cells including TNF-alpha, NO, reactive oxygen intermediates (ROI), and Fas ligand (FasL). E1A sensitizes cells to apoptosis by TNF-alpha, and macrophages kill E1A-expressing cells, in part through the elaboration of TNF-alpha. However, E1A also up-regulates the expression of 70-kDa heat shock protein, a protein that inhibits killing by TNF-alpha and NO, thereby protecting cells from lysis by macrophages. Unlike E1A, E7 does not sensitize cells to killing by TNF-alpha, and the effector mechanism(s) used by macrophages to kill E7-expressing cells remain undefined. The purpose of this study was to further define the capacity of and the effector mechanisms used by macrophages to kill tumor cells that express Ad5 E1A or HPV16 E7. We found that Ad5 E1A, but not HPV16 E7, sensitized tumor cells to lysis by macrophages. Using macrophages derived from mice unable to make TNF-alpha, NO, ROI, or FasL, we determined that macrophages used NO, and to a lesser extent TNF-alpha, but not FasL or ROI, to kill E1A-expressing cells. Through the use of S-nitroso-N-acetylpenicillamine, which releases NO upon exposure to an aqueous environment, E1A was shown to directly sensitize tumor cells to NO-induced death. E1A sensitized tumor cells to lysis by macrophages despite up-regulating the expression of 70-kDa heat shock protein. In summary, E1A, but not E7, sensitized tumor cells to lysis by macrophages. Macrophages killed E1A-expressing cells through NO- and TNF-alpha-dependent mechanisms.     

Transduction of the mammary epithelium with adenovirus vectors in vivo

Because the mammary parenchyma is accessible from the exterior of an animal through the mammary duct, adenovirus transduction holds promise for the short-term delivery of genes to the mammary epithelium for both research and therapeutic purposes. To optimize the procedure and evaluate its efficacy, an adenovirus vector (human adenovirus type 5) encoding a green fluorescent protein (GFP) reporter and deleted of E1 and E3 was injected intraductally into the mouse mammary gland. We evaluated induction of inflammation (by intraductal injection of [(14)C]sucrose and histological examination), efficiency of transduction, and maintenance of normal function in transduced cells. We found that transduction of the total epithelium in the proximal portion of the third mammary gland varied from 7% to 25% at a dose of 2 x 10(6) PFU of adenovirus injected into day 17 pregnant mice. Transduction was maintained for at least 7 days with minimal inflammatory response; however, significant mastitis was observed 12 days after transduction. Adenovirus transduction could also be used in the virgin animal with little mastitis 3 days after transduction. Transduced mammary epithelial cells maintained normal morphology and function. Our results demonstrate that intraductal injection of adenovirus vectors provides a versatile and noninvasive method of investigating genes of interest in mouse mammary epithelial cells.     

Glucagon-like peptide-1 receptor signaling modulates beta cell apoptosis

Glucagon-like peptide-1 (GLP-1) stimulates insulin secretion and augments beta cell mass via activation of beta cell proliferation and islet neogenesis. We examined whether GLP-1 receptor signaling modifies the cellular susceptibility to apoptosis. Mice administered streptozotocin (STZ), an agent known to induce beta cell apoptosis, exhibit sustained improvement in glycemic control and increased levels of plasma insulin with concomitant administration of the GLP-1 agonist exendin-4 (Ex-4). Blood glucose remained significantly lower for weeks after cessation of exendin-4. STZ induced beta cell apoptosis, which was significantly reduced by co-administration of Ex-4. Conversely, mice with a targeted disruption of the GLP-1 receptor gene exhibited increased beta cell apoptosis after STZ administration. Exendin-4 directly reduced cytokine-induced apoptosis in purified rat beta cells exposed to interleukin 1beta, tumor necrosis fator alpha, and interferon gamma in vitro. Furthermore, Ex-4-treated BHK-GLP-1R cells exhibited significantly increased cell viability, reduced caspase activity, and decreased cleavage of beta-catenin after treatment with cycloheximide in vitro. These findings demonstrate that GLP-1 receptor signaling directly modifies the susceptibility to apoptotic injury, and provides a new potential mechanism linking GLP-1 receptor activation to preservation or enhancement of beta cell mass in vivo.     

Reproductive fitness and quinone content of Caenorhabditis elegans clk-1 mutants fed coenzyme Q isoforms of varying length

Caenorhabditis elegans clk-1 mutants lack coenzyme Q9 and accumulate the biosynthetic intermediate demethoxy-Q9. A dietary source of ubiquinone (Q) is required for larval growth and development of the gonad and germ cells. We considered that uptake of the shorter Q8 isoform present in the Escherichia coli food may contribute to the Clk phenotypes of slowed development and reduced brood size observed when the animals are fed Q-replete E. coli. To test the effect of isoprene tail length, N2 and clk-1 animals were fed E. coli engineered to produce Q7, Q8, Q9, or Q10. Wild-type nematodes showed no change in reproductive fitness regardless of the Qn isoform fed. clk-1(e2519) fed the Q9 diet showed increased egg production; however, this diet did not improve reproductive fitness of the clk-1(qm30) animals. Furthermore, animals with the more severe clk-1(qm30) allele become sterile and their progeny inviable when fed Q7-containing bacteria. The content of Q7 in the mitochondria of clk-1 animals was decreased relative to Q8, suggesting less effective transport of Q7 to the mitochondria, impaired retention, or decreased stability. Additionally, regardless of E. coli diet, clk-1(qm30) animals contain a dysfunctional dense form of mitochondria. The gonads of clk-1(qm30) worms fed Q7-containing food were severely shrunken and disordered. The differential fertility of clk-1 mutant nematodes fed Q isoforms may result from changes in Q localization, altered recognition by Q-binding proteins, and/or potential defects in mitochondrial function resulting from the mutant CLK-1 polypeptide itself.     

Oxidase domains in epothilone and bleomycin biosynthesis: thiazoline to thiazole oxidation during chain elongation

The natural products epothilone and bleomycin are assembled by hybrid polyketide/nonribosomal peptide synthetases. Of note in these assembly lines is the conversion of internal cysteine residues into thiazolines and their subsequent oxidation to heteroaromatic thiazole rings. We have excised the EpoB oxidase domain, EpoB-Ox, proposed to be responsible for thiazoline to thiazole oxidation in epothilone biosynthesis, and expressed it in soluble form in Escherichia coli. The purified domain is an FMN-containing flavoprotein that demonstrates thiazoline to thiazole oxidase activity when incubated with thioester substrate mimics. Kinetic parameters were determined for both thiazoline and oxazoline substrates, with k(cat) values ranging between 48.8 and 0.55 min(-1). While the physiological electron acceptor is not yet known, molecular oxygen is needed in these in vitro assays to mediate reoxidation of reduced FMN. Additionally, the oxidase domain-containing BlmIII from the bleomycin assembly line was heterologously expressed and purified. BlmIII is also an FMN-containing protein with activity similar to EpoB-Ox. This work marks the first direct characterization of nonribosomal peptide synthetase oxidase domain activity and will lead to further exploration of these flavoproteins.     

Large-scale propagation of a replication-defective adenovirus vector in stirred-tank bioreactor PER.C6 cell culture under sparging conditions

Large-scale propagation of replication-defective adenovirus vectors has not been well studied to date. One of the challenges for efficient propagation at large scale is to overcome the sensitivity of virus infected cells to gas sparging required for oxygenation and CO(2) removal. In our initial experiments, it was observed that productivity of an adenovirus vector was significantly reduced under sparging conditions as compared to nonsparged, i.e., surface-aerated controls in serum-free cultures. Investigations led to the identification of a buffer containing surfactant (Polysorbate-80, PS-80) that was included in the virus seed stock formulation and introduced through virus infection into the culture at a very low concentration as the cause of the reduced virus productivity. This finding was not obvious and trivial, as neither uninfected sparged nor infected nonsparged PER.C6 trade mark cells in serum-free cultures were affected by the buffer at such a low PS-80 concentration of 0.00025% (v/v), which is a common component of serum-free cell culture media. These results strongly suggest that virus-infected cells behave very differently from uninfected cells under sparging conditions. To mitigate the deleterious effects of sparging, the virus seed stock was prepared in the absence of the buffer containing PS-80. At the same time, the concentration of Pluronic-F68 (PF-68) in the serum-free medium was increased to 1 g/L, at which cell growth and metabolism were unaffected, even though this measure alone did not result in virus productivity improvement. Only by implementing the two measures together was virus productivity loss completely eliminated under sparging conditions. After demonstration of the process robustness in 2-L bioreactors, this adenovirus propagation process was successfully scaled up to 250 L in a 300-L bioreactor under the worst-case sparging conditions projected for 10,000-L scale.     

Serum-free suspension cultivation of PER.C6(R) cells and recombinant adenovirus production under different pH conditions

PER.C6(R) cell growth, metabolism, and adenovirus production were studied in head-to-head comparisons in stirred bioreactors under different pH conditions. Cell growth rate was found to be similar in the pH range of 7.1-7.6, while a long lag phase and a slower growth rate were observed at pH 6.8. The specific consumption rates of glucose and glutamine decreased rapidly over time during batch cell growth, as did the specific lactate and ammonium production rates. Cell metabolism in both infected and uninfected cultures was very sensitive to culture pH, resulting in dramatic differences in glucose/glutamine consumption and lactate/ammonium production under different pH conditions. It appeared that glucose metabolism was suppressed at low pH but the efficiency of energy production from glucose was enhanced. Adenovirus infection resulted in profound changes in cell growth and metabolism. Cell growth was largely arrested under all pH conditions, while glucose consumption and lactate production were elevated post virus infection. Virus infection induced a reduction in glutamine consumption at low pH but an increase at high pH. The optimal pH for adenovirus production was found to be 7.3 under the experimental conditions used in the study. Deviations from this optimum resulted in significant reductions of virus productivity. The results indicate that culture pH is a very critical process parameter in PER.C6(R) cell culture and adenovirus production.     

Isolation of three zebrafish dachshund homologues and their expression in sensory organs, the central nervous system and pectoral fin buds

Drosophila dachshund (dac) interacts with sine oculis (so), eyes absent (eya) and eyeless (ey) to control compound eye development. We have cloned three zebrafish dac homologues, dachA, dachB and dachC, which are expressed widely, in distinct but overlapping patterns. Expression of all three is found in sensory organs, the central nervous system and pectoral fin buds. dachA is also expressed strongly in the somites and dachC in the neural crest and pronephros. These expression domains overlap extensively with those of zebrafish pax, eya and six family members, the homologues of Drosophila ey, eya and so, respectively. This is consistent with the proposal that Dach, Eya, Six and Pax family members may form networks, similar to that found in the fly eye, in the development of many vertebrate organs.